The Online Encyclopedia and Dictionary






Sulfur dioxide



Name Sulfur dioxide
Chemical formula SO2
Appearance Colourless gas


Formula weight 64.1 g/mol
Melting point 198 K (-75 °C)
Boiling point 263 K (-10 °C)
Density 1400 kg/m3 (liquid)
Solubility 9.4 g in 100 g water


ΔfH0gas -296.84 kJ/mol
ΔfH0liquid ? kJ/mol
ΔfH0solid ? kJ/mol
S0gas, 100 kPa 248.21 J/(mol·K)
S0liquid, 100 kPa ? J/(mol·K)
S0solid ? J/(mol·K)


Ingestion Relatively low toxicity, may cause nausea and vomiting. Long term hazards known.
Inhalation Extreme irritation.
Skin Hazardous when cryogenic or compressed.
Eyes Hazardous when cryogenic or compressed.
More info Hazardous Chemical Database

SI units were used where possible. Unless otherwise stated, standard conditions were used.

Disclaimer and references

Sulfur dioxide (or Sulphur dioxide) has the chemical formula SO2. The gas is irritating to the lungs and is frequently described as smelling of burning sulfur.

It is produced by volcanoes and in various industrial processes. In particular, poor-quality coal and petroleum contain sulfur compounds, and generate sulfur dioxide when burned: the gas reacts with water and atmospheric oxygen to form sulfurous acid (H2SO3) and thus acid rain.


Preparation of sulfur dioxide for chemical production

Sulfur dioxide is often prepared by burning sulfur in air:

S(s) + O2 (g) → SO2 (g)

Hydrogen sulfide from crude oil may also be burned.

H2S (g) + O2 {g} → H2 (g) + SO2 (g)

Sulfide ores such as iron pyrites and sphalerite (zinc blende) may also be used:

4 FeS2 (s) + 11 O2 (g) → 2 Fe2O3 (s) + 8 SO2 (g)

2 ZnS (s) + 3 O2 (g) → 2 ZnO (s) + 2 SO2 (g)

When anhydrous CaSO4, is heated with coke and sand in the manufacture of cement, CaSiO3, sulfur dioxide is a by-product.

2 CaSO4 (s) + 2 SiO2 (s) + C (s) → 2 CaSiO3 + 2 SO2 (g) + CO2

Flue gas desulfurisation in power stations releases SO2 for the process.


Sulfur dioxide is sometimes used as a preservative in alcoholic drinks, or dried apricots.

H2SO3 is also called "hydrogen sulfite" or sulfurous acid.

See also:

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Last updated: 10-23-2005 11:50:27
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